Cars today are extremely complex due to the many subsystems that support the reliable performance of high-level functions within a single compact device. The internal combustion engine (ICE), drive train, gearbox, electrical systems, climate-control unit, computational systems, networking devices, passenger compartment, trunk, and additional components all combine to form the overall vehicle. The car body itself has also evolved into a highly sophisticated piece of engineering that fulfills multiple functions, including stability and safety. In particular, the shift to internal combustion engine vehicles has impacted vehicle architecture as a whole. ICE vehicles have one central and embedded propulsion force creating rotational shaft work that is transmitted to the wheels. This vehicle architecture became the paradigm that is still current.
Interest in electric vehicle drive units is resurging with the proliferation of hybrid and electric vehicles. Purely electric vehicles originally used hub mounted motors in the wheel that were easier to handle and more efficiently translated force the wheels. Over time, however, hub mounted electric motors degenerated into an electrical assistance and starter motor for the internal combustion motor. Today's hybrid vehicles utilize more powerful electric drive motors, but still stay within the current paradigm by embedding the electric motor like an ICE. However, the renaissance of hub-mounted electric motors in some purely electric and hybrid cars has not yet led to a fundamental rethinking of vehicle architectures.
Currently emerging key technologies are in-wheel motors, electric braking, integrated steering activators, and active suspension combined with embedded sensors and real time computation. These electric vehicle drive units have the potential to go beyond current applications and lead to novel vehicle architectures and a new vehicle culture. In-wheel motors have been researched extensively and are currently experiencing a renaissance with the development of hybrid and electric cars [Eastham, J. F., Balchin, M. J., Betzer, T., Lai, H. C., and Gair, S, In Proc. ISIE 1995 of the IEEE International Symposium on Industrial Electronics, 2 (10-14 Jul. 1995), pp. 569-573; Zielinski, P., and Schoepp, K., “Three-phase low-speed permanent magnets synchronous Machines”, Institute of Electrical Machine Systems, Technical University of Wroclaw, Poland]. Steering actuators have been placed within-wheels for forklifts and buses. In-wheel suspension and modularity is a well-known principle for platforms carrying heavy loads. Mitsubishi is one of the first large automobile manufacturers to include in-wheel motors in a passenger car, the Colt EV, which is part of a series called the Mitsubishi In-wheel Motor Electric Vehicle (MIEV).
The Michelin Active Wheel consists of a traction motor, a disc brake and caliper, and all active suspension components. The Michelin active wheel does not include a connection point between the wheel and the vehicle, the steering range remains within the traditional limits of +/−30 degrees, and the wheels are not controlled by an autonomous computational device within the wheel.
The Siemens E-Corners makes use of the Electronic Wedge Brake, a pure electronic brake caliper developed by Siemens. A linear motor is built around the brake and a suspension unit is placed in the center of the wheel. A bolt on bracket connects the E-Corner to the vehicle body and allows for the traditional +/−30 degrees of steering range. In contrast to the proposed Robot Wheel design, the Siemens E-Corners do not enable a steering range of up to 150 degrees. Although the Electronic Wedge Brake makes use of an integrated CPU and functions as an information hub in the vehicle data bus system, E-Corners are not intended to function in an autonomous and modular way.
To date, only one concept vehicle has successfully demonstrated the same type of simplicity and multi-functionality as the design principles for wheel robots: the Mini Cooper Concept Car modified by Printed Motors, Ltd. (PML) (2006). The PML car is the first widely known concept vehicle with a simple, multifunctional, in-wheel motor design. This vehicle showcases the capabilities of PML's electric in-wheel motors and their multifunctionality. Not only do the in-wheel motors accelerate and decelerate the vehicle, they also brake. In other words, the PML car has no dedicated braking system because the in-wheel motors are powerful enough to perform the functions of a traditional brake system. Although the PML car uses one-of-a-kind, hand-made electric motors the specifications of the series in-wheel motors prove the feasibility of designing a safe vehicle without brakes. The PML in-wheel motors allow for up to 640 nm of stall torque (30 sec max) which can be used for acceleration or deceleration. Also, each in-wheel motor weighs only 18 kg despite an oversized, conventional five-bolt wheel bearing. The weight is comparable to a conventional wheel bearing disc brake assembly, which means the unsprung or rotational mass is not increased by the in-wheel motors. Thus, the PML car fulfills three roles in the electric vehicle: acceleration, deceleration, and power generation through regenerative braking. These goals are accomplished without increasing the unsprung mass of the wheel assembly.
U.S. patent application Ser. No. 11/153,601, filed Jun. 15, 2005 (U.S. Pat. App. Pub. No. US2006/0012144; Kunzler et al., Jan. 19, 2006), of which the present application is a continuation-in-part and which is incorporated by reference herein in its entirety, discloses the first hubless design for a wheel robot. The Kunzler et al. approach mainly focuses on several in-wheel suspension mechanisms to reduce the unsprung and rotational mass. It permits the motor and other heavy components to remain stable while only the rim, tire, and wheel bearing are unsuspended. The suspension travels vertically along two shafts. A third shaft transmits the drive force via a gear that slides on the shaft's triangular cross section. The design uses a hubless wheel bearing which makes the center of the wheel available for other components.